A controller sometimes uses signals from remote environmental sensors. Typically the controller and the sensor communicate through a hard-wired connection. Many times the hard-wired connection uses the same pair of wires to supply power to the sensor, as it does to communicate information back to the controller. Other times separate wires are used for power and control. One of the reasons the communications link is typically a hard-wired connection is the fact that many times the controller is installed in a vandal-resistant metal cabinet that shields radio frequency (RF) signals, making it impractical to use a wireless communications link. Another reason that the communications link is typically a hard-wired connection is that an RF receiver circuit typically costs significantly more than a simple hard-wired receiver circuit.
Controllers conventionally retrieve data from the remote sensor using the two-conductor hard-wired connection. Typically a pair of wires carries both an excitation voltage to power the sensor as well as data in the form of a modulated current draw. Data containing environmental information of interest is communicated to the controller by modulating the amount of current drawn by the environmental sensor that is sending the data. Current modulation is typically more noise tolerance and affected less by long wire runs than a voltage modulated signal.
An irrigation controller sometimes uses signals from remote environmental sensors that detect rain events, temperature, solar radiation, wind speed, humidity, soil moisture, evapotranspiration, flow, or other parameters.
A lighting controller may use signals from remote sensors to determine when, for how long, in what area, and how bright lights are turned on. These sensors may include ambient light, motion, temperature, precipitation, or other sensors.
In one scenario an ambient light sensor would determine when a desired level of darkness occurred and turn on the lights at that time. Since many times parts of the area to be lighted are more shaded than others, it may be possible to install an ambient light sensor in each area, and individually control the lights in that area.
In another scenario, a motion sensor may determine when there is movement and alert the lighting controller. The lighting controller may respond to this signal by turning on some or all of the lights. Multiple motion sensors could be deployed to allow lights in certain area's to turn on when motion is sensed just in that area. In other embodiments, detected motion may cause lights to turn on if the ambient light is below a certain level.
In yet another scenario, a lighting controller might use a temperature sensor to determine if the ambient temperature is below a certain threshold, and if it is, slowly ramp the intensity of the lights. In another scenario, if snow is sensed, the lights might be turned to warm the light fixture and prevent the snow from building up on it.
Foregoing sensors or combinations thereof would typically be hard-wired into the lighting controller. Frequently, a pair of wires carries both excitation and data in the form of current draw. This is case with the ambient light sensor used with the LX-150 and LX-300 lighting controllers sold by FX Luminaire of San Marcos, Calif. It is also possible for an RS485 bus to be used for communication. Such is the case for the LUXOR Lighting Controller also sold by FX Luminaire. An RS485 bus would modulate voltage to communicate, and while power may be extracted from the bus itself, it may also be supplied via conductors separate from those carrying the data.